The invention relates to new and useful improvements in a counterbalance device. More particularly, the invention relates to a counterbalance device for a medical X-ray unit, with a drum which is at least partly encapsulated in a housing. The drum is mounted so that it can rotate in the housing on a stationary shaft and is provided with an integrated first spring element which applies a bias to the drum. The drum is further provided with a cable which supports a weight, which is guided in a groove on the drum, and which can be wound around or unwound from the drum.
Similar counterbalance devices are used in the medical equipment industry, for example, to counterbalance the dead weight of an X-ray emitter located on a telescoping column guided in the ceiling, so that the height of the X-ray unit can be easily and simply adjusted manually or by mechanical means. Such a device is described in DE 43 11 802 A1 and in DE 44 20 192 A1, for example. As a result of the bias applied by a spring element, a force which opposes the weight of the X-ray emitter is applied to a cable, and results in a counterbalancing of the weight of the unit. It thereby becomes possible to move the weight easily by applying only a small amount of force. Such a counterbalance unit must comply with a number of requirements, particularly in terms of safety. The unit should guarantee that, in the event of any failure or malfunction of the device, the weight does not descend in an uncontrolled and undecelerated manner, which could not only damage the portion of the device being supported or the unit which contains this device, but naturally could also injure a patient who might be lying underneath the weight. Such a failure or malfunction could occur due to the spring element as well as the cable. The prior art, however, does not describe a counterbalance device which fully and satisfactorily meets all safety requirements.